Determination of the concentration of certain components, especially glucose in biological fluids, has been considerably improved by the use of amperometric sensors using an electrode coated with a mediator and with an enzyme specific to said component, for example glucose oxidase, for the detection of glucose. These sensors thus make it possible to measure the transfer of electrons passing between the enzyme and the electrode by the intermediary of the mediator, this electron transfer being proportional to the amount-of component present in the sample of the biological fluid to be tested.
The quality of these sensors, i.e., their accuracy, the reproducibility of the results given by several sensors of the same series, their reliability and the speed of their response time largely depends upon the mediator used.
Mediators known to date, for example from U.S. Pat. No. 4,545,382 of Genetics International, include polyviologen, chloranil, fluoranil or ferrocene.
These mediators have, however, a certain number of disadvantages.
Because they do not transfer the electrons between the enzyme and the electrode sufficiently quickly, the response time of the sensor is rather long. In addition, some of these mediators, such as ferrocene, are relatively volatile or unstable, particularly when exposed to light and the sensors have to be stored under rather strict lighting and temperature conditions. In addition some mediators, especially ferrocene, decompose in water by hydrolysis which is a disadvantage when the sensors are used in blood.
Finally, oxygen enters into competition with some of these mediators and the results of glucose concentration measurements vary according to the amount of oxygen present in the blood. This can be a disadvantage depending on whether venous or arterial blood is being examined.